PURPOSE: To readily provide a platinum complex useful as a carcinostatic agent in a short time by reacting a tetravalent platinic acid salt with 2- aminomethylpyrrolidine and subsequently with oxalic acid silver salt and 1,1- cyclobutanedicarboxylic acid calcium salt.

CONSTITUTION: A tetravalent platinic acid salt is reacted with 2- aminomethylpyrrolidine or an optically active isomer thereof to give a tetrahalogeno (2-aminomethylpyrrolidino) platinum (IV) or an optically active isomer thereof, which is suspended in water and subsequently reacted with two equivalents of oxalic acid silver salt at 60-100°C for 1-2hr to give a compound of formula II. The compound of formula II is reacted with the same amount or more of 1,1-cyclobutanedicarboxylic acid calcium salt in the aqueous solution to give 1,1-cyclobutanedicarboxylato (2-aminomethylpyrrolidine) platinum (II) or an optically active isomer thereof. The compound of formula I may be reacted with 1,1-cyclobutanedicarboxylic acid silver salt and subsequently reduced.